1. Field of the Invention
The present invention relates to a reproduction apparatus and a reproduction method for reproducing a digital audio signal and an encoded stream signal which are recorded on a recording medium.
2. Description of the Related Art
Conventionally, a digital audio signal which is recorded on recording media such as CDs (compact disks) and DATs (digital audio tapes) is recorded in accordance with a 2 cH/16 bit/PCM recording method. Hereinafter, any digital audio signal which has been recorded in accordance with this recording method will be referred to as a xe2x80x9cPCM digital audio signalxe2x80x9d.
In recent years, techniques for recording digital audio signals on a recording medium such as a CD or DAT, where the digital audio signals are encoded in accordance with a predetermined encoding method, have been developed. Hereinafter, any digital audio signal which has been encoded in accordance with a predetermined encoding method will be referred to as a xe2x80x9cstream signalxe2x80x9d. One known example of such a predetermined encoding method is DTS (digital theater system).
DTS is a standard proposed by Digital Theater Systems, Inc. in the U.S. According to DTS, a multichannel signal of up to 5.1 ch can be encoded at a fixed rate of 1.411 Mbps, which is equal to the bit rate for 2 ch/PCM data to be recorded on a CD. The resultant encoded signal is recorded on a CD. Hereinafter, any stream signal which has been encoded in accordance with DTS will be referred to as a xe2x80x9cDTS stream signalxe2x80x9d.
In the case where a PCM digital audio signal is recorded on a CD, the signal recorded on the CD can be reproduced by subjecting the PCM digital audio signal to a D/A (digital to audio) conversion. On the other hand, in the case where a stream signal is recorded on a CD, the stream signal must first be decoded and then subjected to D/A conversion; otherwise, the signal recorded on the CD cannot be reproduced.
Conventionally, it has been impossible to determine whether a signal which is recorded on a CD is a stream signal or a PCM digital audio signal without decoding the signal recorded on the CD. Therefore, there has been a problem in that an undecoded stream signal may be subjected to D/A conversion resulting in unwanted noise being output from the reproduction apparatus.
The aforementioned noise will not be output in the case where the reproduction apparatus includes an internal decoder for decoding a signal which is recorded on a CD, because any stream signal will be decoded by the decoder before being subjected to D/A conversion. However, substantial resources are required to implement such a decoder, resulting in an increase in the cost associated with the reproduction apparatus having an internal decoder.
A reproduction apparatus according to the present invention includes: a signal input section for receiving an input signal having an input signal type; a synchronization signal detection section for detecting a predetermined synchronization signal in the input signal and determining the input signal type in accordance with an occurrence frequency with which an interval repeatedly occurs between adjacent instances of the predetermined synchronization signal; and a signal processing section for subjecting the input signal to a signal processing which is suitable for the determined input signal type.
In one embodiment of the invention, the synchronization signal detection section determines whether or not the input signal is a stream signal containing the predetermined synchronization signal, and if the input signal is a stream signal, the signal processing section performs a signal processing for suppressing a signal level of the input signal.
In another embodiment of the invention, the synchronization signal detection section determines whether or not the input signal is a stream signal containing the predetermined synchronization signal, and if the input signal is not a stream signal, the signal processing section performs a signal processing for boosting a signal level of the input signal.
In still another embodiment of the invention, the synchronization signal detection section includes: a data counter for counting a data amount in the input signal and outputting an address in the input signal; a synchronization signal detector for detecting the predetermined synchronization signal in the input signal and outputting a detection signal representing a result of the detection; an address storage section for storing a plurality of addresses output from the data counter in an address table in response to the detection signal; and an address analysis section for calculating an address interval between adjacent addresses among the plurality of addresses stored in the address table and calculating an occurrence frequency of the address interval, and determining the input signal type based on the calculated occurrence frequency of the address interval.
In still another embodiment of the invention, the address storage section deletes from the address table any past addresses which go back in an address history beyond a predetermined range from a current address.
In still another embodiment of the invention, the predetermined range is set in a variable manner.
In still another embodiment of the invention, in a case where a limited variety of the address interval is previously known to have a possibility of occurring, the address analysis section determines the input signal type in accordance with the occurrence frequencies with which the limited variety of the address interval occurs.
In still another embodiment of the invention, the reproduction apparatus further includes an input section controller for controlling the signal input section so as to read the input signal from a predetermined read position, and a host controller for controlling the input section controller and the signal processing section, wherein: the signal input section reads the input signal ahead from a predetermined position which is beyond a predetermined region from the beginning of the input signal: when the input signal is read from the predetermined position, the host controller places the signal processing section under a default control; the synchronization signal detection section determines the input signal type based on the input signal as read from the predetermined position; the signal input section reads the input signal from the beginning of the input signal after the input signal type has been determined; and the host controller controls the signal processing section so as to subject the input signal to a signal processing which is suitable for the determined input signal type.
In still another embodiment of the invention, the reproduction apparatus further includes an input buffer for temporarily storing the input signal, wherein the synchronization signal detection section detects the predetermined synchronization signal in the input signal stored in the input buffer.
A reproduction method according to the present invention includes the steps of: receiving an input signal having an input signal type; detecting a predetermined synchronization signal in the input signal and determining the input signal type in accordance with an occurrence frequency with which an interval repeatedly occurs between adjacent instances of the predetermined synchronization signal; and subjecting the input signal to a signal processing which is suitable for the determined input signal type.
Thus, the invention described herein makes possible the advantage of providing a reproduction apparatus and a reproduction method which make it possible to identify an input signal type without decoding the input signal, thereby reducing noise in the reproduced signal.
This and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.